Declaration blocks begin with a left curly brace, {, and end with a right curly brace, }. They contain zero or more declarations separated by semicolons:

h2 {
 color: #666;
}

A declaration block is always preceded by a selector. We can combine multiple rules that have the same selector into a single rule. Consider these rules:

h2 {
  color: #666;
}
h2 {
  font-weight: bold;
}

They’re equivalent to the rule below:

h2 {
  color: #666;
  font-weight: bold;
}

Although the last semicolon within a declaration block is optional, it’s good practice to include it, as it’ll help you avoid syntax errors in the future. As you start to add declarations to a block, it’s all too easy to forget the semicolon.